Regulation of electric motors.



v PATENTED APR. 9,,1907.

R. STEBBINS.

' REGULATION OF ELECTRIC MOTORS. A APPLICATION FILED NOV. 9, 1906.

VW/TNESSE I :IZVEMTOR II//I/I,II n By AJTOHNEY PATENT ()FFICE.

HEQGULATION OF ELECTRIC MOTORS.

To (17/ whom if may con /7'71.-

Be it known that I. liowmxn S'rsmnxs. a eitizenol' the I mted States.and a resident of the city of- New York. in the State of Xew' 'YOl'li.ltzlVC'lllVtlltttl certain new and useful lmprovements in llegulationo1' Electric Motors. of wlnch the following is a speeltication.

.\ly present nvention relates to the regulation of electric motors. andhas particular reference to the operation of motors driven by directcurrent.

lt has for its object to preserve constant I the speed of such motorsprovided with a shunt field-magnet winding within more restrieted limitsthan any which I believe to have been attained llCI'UlUl tJl'U.

Certain classes ot electric machinery are required to be driven at asnearly as poss ble uniform speed, andt hese are generally driven byshunt-motors, the speed charaeterlstlc of which is quite uniform withoutexterior regulation. 1thv changes of load, however,

- changes do occur even with shunt-motors.

Some sorts of booster having compound windings and wlnch aremotor-drivel't arealso required to have very stable speeds, as does Imachinery in cotton-nulls and snmlar mstalt lations. To restrictvariations which may pccur. therefore. even with a well-des1gnedshunt-motor, I arrange a regulator which consists of a small generatordriven by the motor and an electromagne-t in circuit with the ingswitchconnected to a substantial resistance in the held-magnet circuit of themain motor. hen the speed tends to rise, the

resistance is cut out, and the field is substan tially strengthened,this being ell'ected bythe increased current delivered by the regulatinggenerator-artnat'ure when its speedis in-' creased. ance is againincluded in the circuit, and the lield is weakened. By certain devices,presently to he described, these effects may be produced withinpractically any restricted range of motor speed that may be selected.

The accon'nmnying drawing is a diagram showing my invention as appliedto any standard apparatus, the particular construction ofwhich of courseis 0 herwise iminaterial.

In the drawing. A is the armature of the Specifieation of LettersPatent.

Application filed November 9. 1906.

generator which operates a short-circuit- When the speedfalls, theresist- Patented April 9, 1907.

Serial No.342,651.

understood.

B is the shunt field-magnet circuit of the motor, connected across thebrushes in the common way. and B is its series field, a com- )ound-woundmachine bein shown thou 'h Y the invention is applicable, as alreadystated, to a pure shuntanotor, while C is a resistance serving toregulate the strength of the field, as presently described.

' I) is the armature of the generator used as a regulator, andv D is itsshunt-field, connected through a resistance E of the potentiometertype,by which the regulation of the [ield may be very closely effected,this forming one of the means determining the limits within which thespeed of the main motor may vary.. The advantage of this form ofresistance is that when the wire thereof is of substantially constantresistance per unit of l length the change in the strength of the field.produced by the winding I) may be almost incrementally regulated anddoes not-proceed by steps or a greater or less amount, as in theordinary forms of rheostat.

with small ehangesof output, aseries coil D 51s arranged upon theheld-magnet of the generator, so that all ot the current passing ibedescribed, passes also through this coil. j By preference thegeneratorwill be slightly 1 -t)"GICOlllPUUhtlCtl, so as to increase therapidity of the changes of output due to change of speed. The armaturesof the motor and the regulating-generator may be upon the same shaft orthey may be geared together in any l convenient way; but in general Iprefer to 1 gear up the small generator so that its speed of revolutionmay be considerably greater generator, having only to supply current ona very restricted scale, may be quite small. In practice a properlywound and connected aregulator.

The field-magnet of the main motor should be worked below the bend ofthe. saturation curve; butit need not contain so much iron as to beuneconornical. magnet of the generator should be w rked well. belowsaturation, as this makes it more responsive to changes in speed of itsarmature, and under some circumstances,

where the speed regulation is to be very no In order to make the fieldvary rapidly to the 'electrom agnets F andG, presently to.

. than that of the mam motor, and thus the.

.lan-motor is of a size well adapted foruse as IcO Preferably the fieldlo 5 F is the armature.

close indeed, the field-magnet ma be laminated with good effect, sincein t is way it will respond substantially without lag.

' F is the coil of an electromagnet of which 7 Contacts ff, connected bythe leads 3 4 to the ends of the resistance C, form with the armature F,which carries one of them, a short-circuiting switch for the resistance.I

Another part of my invention. operated in conjunction with my improvedspeed-regulator is now to be described. The ordinary circuit-breaker His connected in the usual manner in the main lead to the motor and openswhen too large a current flows in the circuit, as is wellunderstood. Thecircuitbreaker is inoperative when for any reason the current fallsbelow' normal, except in' those forms in which the circuit is broken byspecial devices on an entire failure of. current. It now with thecompound-wound motor illustrated a heavy load is being operated and issuddenly thrown ofi, the entire effect of the series field-magnet coil Bis removed and the field greatly weakens. The shunt field-magnet windingwill correct this difliculty, but takes an appreciable time to act onaccount of itslarge inductance tending to prevent a rapid change ofcurrent. Other causes of undue rise of speed, such as a broken lead tothe shunt field-ma net winding, dirt upon the contacts ff, or thesticking of the armature F, or anything else which would prevent theproper operation of the short-circuiti'ng contacts, are also providedfor by theoperation of this part of my invention.

The circuit-breakerH is provided with an auxiliary coil G, whichoperates the trip G This coil is arranged in series with the serieswinding upon the field-magnet of the regulating-generator D, If new theoutput of the generator increases, due to change in speed, beyond suchan amount as can be taken care of by the regulating-magnet F, the coil G(which may be calibrated in the usual manner by adjusting the tension ofthe spring-holding the trip closed) will overcome the resistance of thespring and operate the trip G, thus opening the circuit-breaker andpreventing a disastrous rise of speed.

The principle of operation of my invention is, in brief, greatlyincreasing the field magnetism of the motor whenever it tends to runabove its normal speed and greatly diminish-' ing the field whenever themotor lowers its speed. -Having this in view, it is best to wind thefield-magnet so that the magnetization when the resistance is cut out isslightly above that at' which the normal speed of the motor would beobtained. This gives an immediate response to change of condition causedby the cutting out of the resistance, and in combination, with thecompound winding of the generator (which may be overcompounded with goodeffect) causes the contacts ff to hem a constant state of the motor atvery nearly constant speed.

The usual arrangement for adjusting the positions of the armature F andthe tension of its springmay be employed as an additional meansdetermining the limits within which the speed of the motor may vary.These devices, however, are well understood and require neitherdescription nor illustration.

Having thus described my invention, what I claim, and wish to protect byLetters Patent of the United States, is'

1. The combination, with a continuouscurrent electric? motor having ashunt fieldmagnet winding, and the s 'eed of which is to be maintainedsubstantially constant, of a resistance in series with the field-magnetwinding and of. such amount that the change in the field produced byitswithdrawal or insertion is greater thanis required to correctvariations of motor speed; and means for inserting or withdrawing theentire resistance at once, such means responsive to changes in the motorspeed.

2; The combination, with an electric motor to be operated at constantspeed, of a field-magnet winding, a resistance incircuit therewith ofamount such that the change in the field caused by its insertion orwithdrawal is greater than is required to correct variations of themotor speed; an electrically-operated switch for cutting in or cuttingout the resistance, and means, responsive to changes in the motor speed,for cutting in the entire resistance at once as the speed falls and forso cutting it out as the speed rises.

'3. The combination, with an electric motor provided with a field-magnetwinding and a resistance in circuit with said winding, of a switchhaving contacts and connections for shunting the resistance; and agenerator rotated by the motor, the current from which operates theswitch.

4. The combination, with a motor provided with a shunt field-magnetwinding, of a resistance in series with such field-magnet winding, aswitch having contacts and connections for shunting the resistance, anelectromagnet controlling the switch, and a generator operated by themotor, the current from which controls the electromagnet.

5. The combination, with a motor having a shunt field-magnetwinding, ofa resistance in series with said winding, a switch having contacts andconnections for shunting the resistance at. desired times, theresistance being of an amount in excess of that required to compensatefor variations in the desired speed of the motor, and electrical means,responsive to such changes in speed, for operl ating the switch atdesired times.

6. The combination, with a motor having vibration, the net result ofwhich is to keep a shunt field-magnet winding, of aresistance in serieswith said winding of such amount as to cause by its insertion orwithdrawal a change in the field in excess of that required to controlthe speed of the motor; means for shunting the resistance, anelectromagnet for operating such means, and a generator driven by themotor, the changes in the output of which due to change in speed causethe electromagnet to open and close the shunt.

7. The combination, with a motor having a shunt-winding, of a generatordriven by the motor, a resistance in circuit with a shunt field-magnetwinding, 'a switch for inserting or cutting out the resistance, "and anelectromagnet in circuit with the generator and controiling the switch.

8. In combination with a motor, having a shunt-winding, a generatordriven by the motor, means for determining the output of the generator'at' given speed, a resistance in the shunt field-magnet circuit of themotor;

and means, responsive to changes in the generator outputdue to change111 speed, for cutting out or inserting the resistance.

'9. The combination with a motor having a shunt field-magnet winding andthe speed of which is to bemaintained substantially constant, of agenerator driven thereby and so geared that its speed changes with andover -wider limits than that of the motor; and

means 'for changing the motor speed, in-

versely responsive. to the changes of speed of I 5 the generator.

10. The combination, with-a shunt-wound motor, of a compound -woundgenerator iven by the motor and-so geared as to rotate faster than themotor revolves; a resistance in the motor field-magnet circuit, an,

electromagnet in circuit with the generatorarmature, and a switchcontrolling the'resistance and operated by the electromagnet.

. 11. The combination, with'a motor having a shunt field-magnet Winding,of a generator driven bythemotor and having a fieldmagnet winding with aresistance of the by the motor, the changes in the output of whichoperate the regulator, of a circuit-breaker in themotor-lead and meansfor causing the changes of the generator-current to operate thecircuit-breaker when the regulator fails to operate.

In witness whereof I have hereunto set my namein the presence of twowitnesses. ROWLAND STEBBINS. Witnesses:

T. J. JOHNSTON, ANITA BURKE.

